The transmission of data via optical systems is performed by imparting information in some manner onto an optical signal. Optical modulators may be used to convert an electrical information carrying signal into an optical modulated signal. Currently, modulators are either athermal (i.e., not affected by changes in operating temperature of the system, which may include modulator and/or light source) and consume high power, or are highly temperature dependent (i.e., readily affected by changes in operating temperature of the system) and consume low power.
FIG. 1 is a diagram of a Mach-Zehnder Interferometer (MZI) as known in the prior art. Modulator 100 includes optical waveguide splitter 110, optical waveguide re-combiner 120, and optical waveguide branches 130 and 140, each branch including optically active material. Electrodes 135 and 145 are associated with waveguide branches 130 and 140, respectively.
Modulator 100 receives light from a light source (e.g., a laser) to optical waveguide splitter 110 in order for the light to travel along branches 130 and 140. The reunited beam exits the modulator at the end of optical waveguide re-combiner 120. An electrical voltage applied to electrodes 135 and 145 provides a phase change in the light propagating through branches 130 and 140 (i.e., the refractive index of the optically active material will change based on the voltage applied to the electrodes).
Thus, when no modulating voltage is applied to either of the electrode sets, light traveling along branches 130 and 140 arrives at re-combiner 120 in-phase. If a voltage is applied to one of the electrode sets, a differential change occurs due to the electro-optic effect, and the signals arrive at re-combiner 120 out of phase. By controlling the modulation voltage to one, or both of the electrode sets, MZI 100 may be operated to convert a continuous wave into a high bit rate modulated signal.
For high frequency performance, the electrodes of the modulators need to be short in device length in order to obtain high-speed due to the total device capacitance. If the electrodes are not sufficiently short, to improve the efficiency of modulation while keeping a high modulation frequency, the light wave and the electrical signal (a radio-frequency electromagnetic wave) may be made to co-propagate in the material. Optoelectronic devices employing co-propagation of light and electrical signals belong to a class known as traveling-wave devices; however, traveling-wave devices consume more power, and the complexity of their structure is not ideal for mass-production.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the invention is provided below, followed by a more detailed description with reference to the drawings.